In the semiconductor device, an integrated circuit has become highly integrated, and a DRAM has required the reduction of size and the enlargement of memory capacity of a memory cell. For this requirement, an MIM (metal-insulator-metal) structure capacitor has been spotlighted. Such a MIM structure capacitor uses a high dielectric material, such as strontium titanate (SrTiO3), as an insulating film (dielectric film).
In the formation of a SrTiO3 film for a DRAM capacitor, a method for forming a film by ALD has been conventionally widely used, in which an organic Sr raw material and an organic Ti raw material are used, and O3 gas is used as an oxidant, [for example, “Plasma enhanced atomic layer deposition of SrTiO3 thin films with Sr(tmhd)2 and Ti(i-OPr)4” J. Vac. Scl. Technol. A20(5), J. H. Lee et al. September/October 2002].
However, in forming a thin film by such a method, it is difficult to crystallize the thin film even with a stoichiometric composition of Sr:Ti=1:1 through annealing following the film formation depending on the kind of a substrate. It is preferable that a Sr—Ti—O-based material should be crystallized because it has a low dielectric constant in an amorphous state.
Meanwhile, in ALD, a SrO film forming process by a Sr raw material-purge-oxidant-purge, and TiO film forming process by a Ti raw material-purge-oxidant-purge are alternately repeated to form a film. However, in this method, adsorption may be inhibited according to the combination of raw materials. Accordingly, the composition of the formed film may be different from the required one.
Also, in ALD, the supply time for respective materials and an oxidant is set as a time when a film thickness is saturated. However, when O3 is used as an oxidant, it takes a longer time to reach the saturation point depending on the kind of an organic Sr compound used as a Sr raw material, and the film thickness becomes very thick (0.3 to 0.4 nm) per 1 cycle at the saturation point. This may prevent the required SrO film from being formed.